Migrate display_timezone setting

Dates will be migrated into UTC, the app's timezone will remain as UTC, but the display_timezone will be set to the v2 app's timezone.

Author: duncanmcclean

src/SettingsMigrator.php

@@ -124,6 +124,7 @@ protected function migrateSystem()
 
         Configurator::file($configFile = 'statamic/system.php')
             ->set('multisite', count($sites) > 1)
+            ->set('display_timezone', $system['timezone'] ?? null)
             ->ifNoChanges($this->throwNoChangesException($configFile));
 
         return $this;

tests/MigrateSettingsTest.php

@@ -155,6 +155,11 @@ public function it_migrates_routes()
     /** @test */
     public function it_migrates_system_settings()
     {
+        $this->files->put($this->sitePath('settings/system.yaml'), <<<'EOT'
+timezone: 'America/New_York'
+EOT
+        );
+
         $this->artisan('statamic:migrate:settings', ['handle' => 'system']);
 
         $this->assertSameWithNormalizedLineEndings(File::get(resource_path('sites.yaml')),
@@ -166,6 +171,11 @@ public function it_migrates_system_settings()
 
         $this->assertConfigFileContains('system.php', <<<'EOT'
     'multisite' => false,
+EOT
+        );
+
+        $this->assertConfigFileContains('system.php', <<<'EOT'
+    'display_timezone' => 'America/New_York',
 EOT
         );
     }